J. Nannoplankton Res. 30 (1), 2008, pp.39-49 © 2008 International Nannoplankton Association, Inc.
ISSN 1210-8049 Printed by Cambridge University Press, UK

39

Upper Campanian-Maastrichtian calcareous nannofossil
biostratigraphy of the Stevns-1 borehole, Denmark
Emma Sheldon
Department of Stratigraphy, Geological Survey of Denmark & Greenland (GEUS), Øster Voldgade 10, DK-1350, Copenhagen K, Denmark; es@geus.dk

Manuscript received 6th February, 2008; revised manuscript accepted 6th March, 2008

Abstract The Stevns-1 borehole (Stevns Klint, eastern Denmark) penetrated lowermost Danian bryozoan limestone
and Maastrichtian chalk before reaching a terminal depth of 456.1m in the Campanian/Maastrichtian boundary interval. The borehole, drilled as part of a project to study the Earth System in a Greenhouse World, provides the most complete and expanded section through the Maastrichtian in NW Europe. Consequently, it constitutes a significant
biostratigraphic reference for this interval. This work presents the biostratigraphy of the borehole, underpinningpalaeoecological research that is in progress.
Application of existing northern high-latitude calcareous nannofossil biozonation schemes to the biostratigraphic data
has revealed some previously unsubstantiated/unreported nannofossil events. These include the extinction of Helicolithus trabeculatus and increase in abundance of Prediscosphaera grandis in the Upper Maastrichtian, and extinctionof Zeugrhabdotus praesigmoides in the Campanian/Maastrichtian boundary interval. These may prove to be useful infurther subdividing this interval, or of particular palaeoecological relevance. Additionally, some nannofossil events appear to contradict those of the established schemes, such as higher than expected extinctions of Zeugrhabdotus bicrescenticus and Gartnerago segmentatum, and the lower than expected extinction of Calculites obscurus. The
significance of these, in biostratigraphic or palaeoecological terms, remains to be assessed.
Keywords Calcareous nannofossils, Maastrichtian, Campanian, Boreal Realm, Denmark
1. Introduction
A shallow borehole was drilled and cored, in 2005, throughLower Danian, Maastrichtian and Upper Campanian limestone and chalk at Stevns Klint, on the east coast of Sjælland, eastern Denmark (Figure 1). The operation took place
under the auspices of the Cretaceous Research Centre(CRC), a collaboration of scientists from The Geological
Survey of Denmark and Greenland (GEUS) and the Department of Geography and Geology, University of Copenhagen, and was funded by the Danish Natural Science
Research Council (FNU). The project for which the borehole was drilled aimed to investigate the lithological composition, variation and cyclicity of the Maastrichtian part of
the Chalk Group. The succession comprises ridge, drift,moat and valley systems formed by long-lasting bottomcurrents (Lykke-Andersen & Surlyk, 2004; Surlyk &Lykke-Andersen, 2007). The Stevns-1 borehole (DGU
218.1938) was positioned on a palaeotopographic ridge. It
was drilled from close to the base of the Danian Stevns
Klint Formation into the Maastrichtian chalk of the Tor
Formation below, with the intention of obtaining a complete core through the Maastrichtian (Surlyk et al., 2006).
The succession in the area is expanded, compared with theequivalent succession in the chalks of the North Sea.
Breaks in sedimentation are documented by firmgrounds,
but hardgrounds are not present (S.L. Rasmussen, H.B.
Madsen, pers. comms, 2008). The drilled interval represents the only completely cored section through the Upper
Campanian-Maastrichtian of NW Europe, rendering it ideal
as a biostratigraphic reference section (Stemmerik et al.,2006). Apart from providing a time-frame for current andfuture research (sedimentological logging, nannofossil
palaeoecology, carbon, oxygen and strontium isotopes,
trace elements, silica and diagenesis studies), the data derived from this cored interval is ideal for testing existing
nannofossil zonation schemes, and this is the theme of thework presented here.
Several nannofossil biostratigraphic schemes have beendeveloped from northern high-latitude Campanian and
Maastrichtian sediments, primarily in response to hydrocarbon exploration in the North Sea (e.g. Sissingh, 1977,
1978; Perch-Nielsen, 1979; Crux, 1982). The ‘NK’ biozonation scheme (Mortimer, 1987) was based on successions in the Danish and southern Norwegian sectors of theNorth Sea, using core, sidewall core and ditch-cuttings
samples. This has been superceded by the ‘UCBP’ (Upper
Cretaceous boreal province) nannofossil biozonation
scheme of Burnett (1998), which was developed from thescheme of Burnett (1990), and was based on outcrop andwell sections from Denmark, Germany, Holland, and thenorthern and southern UK. Network Stratigraphic Consulting Limited (hereafter NSCL) have since further refined
the UCBP scheme for more local use, using data from several hundred wells in the Norwegian and Danish sectors of
the North Sea, to erect a number of subzones within the UC
framework, particularly in UC16BP (Campanian/Maastrichtian boundary interval) and UC19-20 BP (Maastrichtian; Fritsen, 1999). Here, I present the results of thenannofossil biostratigraphic study of the Stevns-1 borehole.
These results suggest further, potentially useful biostratigraphic events, and highlight some discrepancies relative tothe established biozonations.

40

Sheldon(Fritsen, 1999), was utilised for
the Maastrichtian and Campanian(Figure 3). It should be noted that
the Lower/Upper Maastrichtianboundary has not been formallydefined, but that the nannofossil
zones of Burnett (1998) have beencalibrated with belemnite zones inGermany, so an approximation
can be made based on the belemnite substage definitions. The baseMaastrichtian has been formallydefined and lies in nannofossil
zone UC16 (Odin, 2001). However, the base cannot be precisely
located in the boreal region because the sequence of nannofossil
events in the boreal region isslightly different from that seen in
the low-latitude boundary-stratoFigure 1: Maps illustrating the location of the Stevns-1 borehole, eastern Denmark. A) Regional geomorphology (after Stemmerik et al., 2006). B) Location (after Surlyk & Lykke-Andersen, 2007)
type section (Tercis, southern
France), and also the nannofossil
2. Materials and methods
event that lies just above the boundary in Tercis is not presThe Stevns-1 borehole is situated near Mandehoved, close ent at all in the boreal region (last occurrence of Uniplato the village of Højerup, eastern Sjælland, Denmark (Fig- narius trifidus), because this is a lower-latitude-restricted
ure 1). The borehole was drilled early in 2005 by Faxe Kalk taxon.
A/S and penetrated 456.1m of lowermost Danian, Maastrichtian and Campanian/Maastrichtian boundary interval 3. Biostratigraphic results
sediments (Figure 2), with close to 100% recovery. The The biostratigraphic data are presented on the range-chart
borehole was terminated in the Campanian/Maastrichtian (Table 1). Rich and diverse nannofossil assemblages charboundary interval, belonging to nannofossil zone UC16aBP. acterise most of the succession. Species richness, excluding
The Cretaceous/Tertiary boundary was picked using the reworked species, is 64 for the Maastrichtian and 71 for the
gamma log (Figure 2).
Campanian/Maastrichtian boundary interval. The nannoA total of 83 samples were analysed, taken at approxi- fossil preservation is, in general, relatively good, particumately every 5m, except around (sub)zonal boundaries, larly when compared to Maastrichtian chalk from thewhere sampling density was, at times, higher. The succes- Danish North Sea (Sheldon, 2006). This is probably due tosion roughly comprises Upper Campanian-lowermost the Stevns area only being buried to a depth of approxiMaastrichtian bioturbated chalk, succeeded by Lower mately 500m during post-Danian times (Japsen & Bidstrup,
Maastrichtian chalk and marl. The Upper Maastrichtian 1999), compared with 2–3km in the Central Graben. The
part comprises almost pure chalk with some intervals of nannofossil biostratigraphic breakdown is discussed below,
flint-rich chalk and marly horizons (marly horizons can be following Burnett (1998), using first downhole occurrences
seen on the gamma log: Figure 2). Bryozoans and other (FDO) and last downhole occurrences (LDO) of key
macrofossils increase towards the top of the Maastrichtian species (Figure 3). Selected zonal marker species are illus(Stemmerik et al., 2006). Nannofossil smear-slides were trated on Plate 1.
prepared from core plugs using the simple smear-slide technique described in Bown & Young (1998). The prepared 3.1 Danian (0-12.47m)
slides were examined using a Leitz Laborlux 8 light-mi- NNTp1B (0-12.47m): The assemblage comprises Daniancroscope, at 1250x magnification. All slides are stored at and survivor nannofossils, including Zeugrhabdotus sigGEUS.
moides, Biscutum spp., Markalius inversus, BraaruDue to the biostratigraphic nature of the study, basic dosphaera
bigelowii,
Neocrepidolithus
cohenii,
presence/absence counting was employed. Particular care Cyclagelosphaera reinhardtii and some Upper Cretaceous
was taken to search for biostratigraphic marker-species, reworked species. The presence of Z. sigmoides, which
and obvious changes in assemblage composition were marks the base of subzone NNTp1B, suggests that the lownoted (Figure 3). A complete taxonomic list is found in ermost Danian (subzone NNTp1A) does not exist here, orBown (1998). The ‘NNTp’ nannofossil zonation scheme of was not sampled.
Varol (1998) was applied to the Danian, whereas the UCBP
scheme of Burnett (1998), with modifications by NSCL

Upper Campanian-Maastrichtian biostratigraphy...Denmark

41

3.2 Maastrichtian (14.29-275.54m)
UC20dBP
(14.29-39.07m):
The
presenceof
Cribrosphaerella daniae indicates UC20dBP. The FDO of
Gartnerago segmentatum (= Gartnerago obliquum of someauthors; Figure 3) is found within this subzone. G. segmentatum occurs more or less consistently from the baseof the cored section to 56.57m, above which it occurs occasionally (Table 1). Reworking is occasionally present in
the form of Reinhardtites levis and Calculites obscurusfrom the Lower Maastrichtian, and Eiffellithus eximius
from the Campanian. These species are considered to be
reworked, as they occur as rare specimens in an occasional
sample (Table 1).
UC20cBP (41.15-94.32m): Common Arkhangelskiellamaastrichtiana, together with the absence of C. daniae, indicates UC20cBP. The FDO of Zeugrhabdotus bicrescenticus (= Zygodiscus compactus of some authors) is foundwithin this subzone (Figure 3). The FDO of Helicolithus
trabeculatus occurs at 94.32m, and may have potential asa biostratigraphic indicator towards the base of this subzone (Table 1). Occasional reworking is represented by
Seribiscutum primitivum and R. levis.
UC20bBP (98.16-132.53m): The presence of Nephrolithus
frequens, together with the absence of C. daniae and A.
maastrichtiana, indicate that this interval belongs to
UC20bBP. N. frequens is not found in the interval from
118.5m to 123.10m in the Stevns-1 borehole. N. frequens is
also absent from intervals within UC20bBP in the Danish
North Sea (Sheldon, 2006). Occasional reworking is represented by R. levis.
UC20aBP (137.14-164.8m): This interval is assigned toUC20aBP based on very rare occurrences of Lithraphidites
quadratus. Prediscosphaera grandis increases in abundance from UC20aBP downhole.
UC19 (174.24-243.09m): The FDO of S. primitivum, together with the absence of L. quadratus, mark the presenceof UC19. It is noted that Biscutum magnum has its FDO
close to that of S. primitivum (Table 1). Poorly-preserved
specimens of S. primitivum (where the central-area is missing) can be difficult to differentiate from B. magnum. Occasional reworking is represented by Tranolithus orionatus
and R. levis.
UC17 (252.31-275.54m): The FDOs of consistent R. levis
and T. orionatus (marker-species for UC18 and UC17, respectively) almost coincide, indicating that UC18 is likely
missing or condensed in this borehole. The FDO of in situ
C. obscurus was noted at 275.54m. According to NSCL
(Fritsen, 1999), this species is used as a marker for base
UC19ii (Figure 3), equivalent to lower UC19 of Burnett(1998).

Figure 2: Stevns-1 depth profile, nannofossil zonation (UCBP zonation of
Burnett, 1998) and gamma log (after Stemmerik et al., 2006)

3.3 Campanian/Maastrichtian boundaryinterval (284.81-456.10m)
UC16dBP (284.81-317.28m): UC16dBP is characterised by
the FDO of Broinsonia parca constricta and continued
presence of the marker-species denoting UC19, UC18 andUC17. NSCL (Fritsen, 1999) use the FDO of Reinhardtities

Sheldon
42

140
145
150
155
160
165
170
175
180
185
190
195
200
205
210
215
220
225
230
235
240
245
250
255
260

141.52151.00155.60164.80174.24178.87184.10187.85192.22196.93201.66210.77220.10224.68229.33234.89238.71243.09252.31254.27256.13257.12261.77265.87270.85275.54284.81
289.67294.13298.66303.39308.03312.57317.28R

R

Table 1: Stevns-1 nannofossil distribution chart

UC20aBP
UC19
UC17
UC16dBP

265
270
275
280
285
290
295
300
305
310
315

Upper Cretaceous
Lower Maastrichtian
Tor Formation

Upper Campanian-Maastrichtian biostratigraphy...Denmark

Period/EpochDanianAge

Chronostrat.

Stevns
Klint
Fm

Formation Lithostrat.

NNTp1B

UC20dBP

UC20cBPInterval: 0m - 456m
Scale: 1:500

Early
Palaeocene

UC20bBP

Stevns-1

Depth
m

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

125

130

135

Upper Maastrichtian43(Sub)zone

Burnett (1998)
Varol (1998)

6.94

12.47
14.29
16.24
17.25

22.10

27.22

36.42
39.07
41.15

46.26

56.57

65.77

75.00

80.71

85.10

90.08

94.32

98.16

104.02113.37123.10118.55132.53137.14

Sample depth is BASE of
depth-range

Sample level (metres)

R

Nannofossil distribution (presence/absence)

R

R

R
R

R

R

R

R
R=Reworked

R

Biscutum harrisonii
Braarudosphaera bigelowii
Cyclagelosphaera reinhardtii
Markalius inversus
Neocrepidolithus cohenii
Thoracosphaera spp.
Zeugrhabdotus sigmoides
Ahmuellerella octoradiata
Arkhangelskiella cymbiformis
Arkhangelskiella maastrichtiana
Chiastozygus amphipons
Cretarhabdus conicus
Cribrosphaerella daniae
Cribrosphaerella ehrenbergii
Eiffellithus gorkae
Eiffellithus turriseiffelii
Kamptnerius magnificus
Lithraphidites carniolensis
Lithraphidites quadratus
Lucianorhabdus cayeuxii
Micula decussata
Nephrolithus frequens
Octocyclus reinhardtii
Placozygus fibuliformis
Prediscosphaera cretacea
Prediscosphaera stoveri
Retecapsa crenulata
Retecapsa surirella
Watznaueria barnesiae
Lithraphidites praequadratus
Microrhabdulus decoratus
Micula cubiformis
Octolithus multiplus
Prediscosphaera grandis
Prediscosphaera spinosa
Staurolithites flavus
Biscutum spp.
Gartnerago segmentatum
Orastrum campanensis
Rhagodiscus angustus
Zeugrhabdotus embergeri
Zeugrhabdotus bicrescenticus
Staurolithites mutterlosei
Discorhabdus ignotus
Rhagodiscus splendens
Staurolithites integer
Staurolithites imbricatus
Rhagodiscus reniformis
Helicolithus trabeculatus
Zeugrhabdotus erectus
Staurolithites laffittei
Broinsonia cf. B. matalosa
Calciosolenia fossilis
Zeugrhabdotus spiralisMarkalius apertus
Seribiscutum primitivum
Biscutum magnum
Loxolithus spp.
Staurolithites mielnicensis
Chiastozygus bifarius
Neocrepidolithus cruciatus
Cyclagelosphaera margerelii
Broinsonia signata
Tranolithus orionatus
Reinhardtites levis
Calculites obscurus
Broinsonia parca constricta
Monomarginatus quaternarius
Reinhardtites anthophorus
Broinsonia parca parca
Zeugrhabdotus praesigmoides
Quadrum gartneri
Watznaueria manivitiae
Tranolithus minimus
Prolatipatella multicarinata
Tortolithus pagei
Heteromarginatus bugensis
Tortolithus hallii
Saepiovirgata biferula
Tortolithus caistorensis
Misceomarginatus pleniporus
Uniplanarius gothicus
Cylindralithus sculptus
Podorhabdus? elkefensis
Eiffellithus eximius
Gartnerago obliquum
Rhagodiscus indistinctus
Staurolithites minutus

44

Sheldon

Period/EpochChronostrat.

Campanian/Maastrichtian boundary interval

AgeInterval: 0 m - 456 m
Scale: 1:500

Stevns-1

320

325

330

335

340

345

350

355

360

365

370

375

380

385

390

395

400

405

410

415

420

425

430

435

440

450

445

TD 455

Depth

Formation Lithostrat.

UC16aBP

UC16b-cBP

SubzoneBurnett (1998)

Sample depth is BASE of depth range

321.76325.77330.29335.00339.36349.77353.90362.80372.00381.45384.18387.88390.73400.00404.76409.45413.00413.98418.65428.03437.29446.67455.95456.10Samples (metres)
Presence/Absence

Biscutum harrisonii
Braarudosphaera bigelowii
Cyclagelosphaera reinhardtii
Markalius inversus
Neocrepidolithus cohenii
Thoracosphaera spp.
Zeugrhabdotus sigmoides
Ahmuellerella octoradiata
Arkhangelskiella cymbiformis
Arkhangelskiella maastrichtiana
Chiastozygus amphipons
Cretarhabdus conicus
Cribrosphaerella daniae
Cribrosphaerella ehrenbergii
Eiffellithus gorkae
Eiffellithus turriseiffelii
Kamptnerius magnificus
Lithraphidites carniolensis
Lithraphidites quadratus
Lucianorhabdus cayeuxii
Micula decussata
Nephrolithus frequens
Octocyclus reinhardtii
Placozygus fibuliformis
Prediscosphaera cretacea
Prediscosphaera stoveri
Retecapsa crenulata
Retecapsa surirella
Watznaueria barnesiae
Lithraphidites praequadratus
Microrhabdulus decoratus
Micula cubiformis
Octolithus multiplus
Prediscosphaera grandis
Prediscosphaera spinosa
Staurolithites flavus
Biscutum spp.
Gartnerago segmentatum
Orastrum campanensis
Rhagodiscus angustus
Zeugrhabdotus embergeri
Zeugrhabdotus bicrescenticus
Staurolithites mutterlosei
Discorhabdus ignotus
Rhagodiscus splendens
Staurolithites integer
Staurolithites imbricatus
Rhagodiscus reniformis
Helicolithus trabeculatus
Zeugrhabdotus erectus
Staurolithites laffittei
Broinsonia cf. B. matalosa
Calciosolenia fossilis
Zeugrhabdotus spiralisMarkalius apertus
Seribiscutum primitivum
Biscutum magnum
Loxolithus spp.
Staurolithites mielnicensis
Chiastozygus bifarius
Neocrepidolithus cruciatus
Cyclagelosphaera margerelii
Broinsonia signata
Tranolithus orionatus
Reinhardtites levis
Calculites obscurus
Broinsonia parca constricta
Monomarginatus quaternarius
Reinhardtites anthophorus
Broinsonia parca parca
Zeugrhabdotus praesigmoides
Quadrum gartneri
Watznaueria manivitiae
Tranolithus minimus
Prolatipatella multicarinata
Tortolithus pagei
Heteromarginatus bugensis
Tortolithus hallii
Saepiovirgata biferula
Tortolithus caistorensis
Misceomarginatus pleniporus
Uniplanarius gothicus
Cylindralithus sculptus
Podorhabdus? elkefensis
Eiffellithus eximius
Gartnerago obliquum
Rhagodiscus indistinctus
Staurolithites minutus

Nannofossil distribution (presence/absence)

R

R
R

R

R

Table 1: Stevns-1 nannofossil distribution chart (continued from previous pages)

Upper Campanian-Maastrichtian biostratigraphy...Denmark

anthophorus as an intra-UC16dBP marker, while Burnett(1998) utilises this bio-event as a marker for base UC16. R.
anthophorus was found as a rare occurrence in one sample
within UC16dBP and is, therefore, not used as a marker
here.
UC16b-cBP (321.76-372.00m): By definition, the FDO of
Monomarginatus quaternarius marks the base of UC16dBP(Burnett, 1998). A single specimen of M. quaternarius wasnoted within UC16dBP, at 294.13m. Due to identificationdifficulties and sporadic occurrences, this species is notconsidered to be a reliable marker in this study. The FDOof Broinsonia parca parca also coincides with the base ofUC16dBP (intra-UC16ii of NSCL; Figure 3), and is found at
321.76m. The FDO of Zeugrhabdotus praesigmoides coincides with the FDO of B. parca parca in this study. Thebase of UC16cBP is defined by the FDO of Tortolithus caistorensis. This species is rare and its FDO occurs belowthat of Heteromarginatus bugensis (which marks the baseof UC16bBP) in the current study. H. bugensis likely preserves preferentially to Tortolithus spp. (J. Lees, pers.
comm., 2008). The former species is therefore preferred asa marker to Tortolithus spp. It is not possible, consequently,
to identify UC16bBP in the Stevns-1 borehole. Tortolithus
pagei has its FDO at 372.00m. Occasional reworking isrepresented by rare Eiffellithus eximius.
UC16aBP (381.45-456.10m): The marker species for base
UC16bBP is H. bugensis, following the Burnett (1998)
zonation. The FDO of H. bugensis also marks the base of
NSCL’s UC16ii (Figure 3). This species is found in thepresent study from 381.45m and downwards. Within thissubzone (UC16aBP), Misceomarginatus pleniporus and M.
quaternarius occur downwards from 390.73m and404.76m, respectively. T. caistorensis is found from387.88m to the base of the core at 456.10m, and Tortolithus
hallii has its FDO at the top of this subzone, at 381.45m.
Tortolithus spp. may act as supplementary subzonal
marker-species in the local Danish onshore area. Reinhardtites levis, Lucianorhabdus cayeuxii and Calculites obscurus become abundant in the lower part of this interval.
Occasional occurrences of E. eximius and Saepiovirgata
biferula within this subzone are considered to be reworked
from UC15 or lower.
UC15: The FDO of E. eximius marks the base of UC16
(Figure 3). This species was found occasionally inUC20dBP, UC16b-cBP and UC16aBP in this study, where it isconsidered to be reworked (Table 1). The FDO of R. anthophorus also marks the base of UC16 in the Burnett(1998) scheme. This species was noted within UC16aBP,
UC16b-cBP and UC16dBP, but identification can be problematic, and it is therefore not used as a marker here. It is
concluded that UC15 may not have been penetrated in the
Stevns-1 borehole.
4. Biostratigraphic discussion
The Stevns-1 borehole data presented here suggest some
biostratigraphic events that differ from those used in theestablished biozonation schemes (Figure 3).

45

Specimens, interpreted as reworked, of Reinhardtites
levis and Eiffellithus eximius are found, sporadically, above
their known ranges in this borehole (Table 1). The Sorgenfrei-Tornquist Zone (Figure 1A) was associated with inversion and uplift during the Cretaceous, and was exposed(Vejbæk & Andersen, 2002; Surlyk & Lykke-Andersen,2007). This probably accounts for the reworking found in
the Stevns-1 borehole.
The FDOs of Gartnerago segmentatum and Zeugrhabdotus bicrescenticus occur in UC20dBP and UC20cBP, respectively, in this study, whereas NSCL use these
bio-events to subdivide UC19. It cannot be ruled out thatthese species are reworked, but the distribution patterns
seen on the range-chart (Table 1) suggest that this is not thecase in the Stevns area; they occur, more often than not, in
successive samples, and not necessarily in samples whereclearly reworked specimens, such as R. levis and E. eximius, are found. It is not unusual that taxa appear sporadically towards the end of their range: Z. bicrescenticus isfound consistently from the base of the core to 252.31m,
followed by a gap of approximately 30m where it is notseen, followed by two intervals (220.01m to 151.00m and
104.02m to 41.15m) where it appears more or less consistently; Table 1).
The marker-species for UC20bBP, Nephrolithus frequens, is not consistently present within this subzone, nor
in UC20cBP. Particular care should, therefore, be taken
when assigning UC20BP in the boreal region. It is inferredthat the pattern that this high-latitude taxon demonstrates isa response to environmental perturbations, such as temperature variation, in the Danish Central Graben and Danish Basin (Sheldon, 2006).
The FDO of Helicolithus trabeculatus occurs within
UC20cBP. The use of Lithraphidites quadratus as a marker
for UC20aBP is relatively limited, as it is extremely rare in
the North Sea (Sheldon, 2006; M. Hampton, pers. comm.,2007). This species is also difficult to distinguish from
Lithraphidites praequadratus in poorly-preserved material.
Prediscosphaera grandis increases in abundance downholefrom UC20aBP. The FDO of Calculites obscurus is found in
UC17 in the Stevns-1 borehole, compared with UC19 in
the NSCL scheme.
The FDOs of R. levis and Tranolithus orionatus almost
coincide, indicating UC18 is either missing or condensed inthis section. It was also noted that UC17 is relatively verythin in this well. The missing section is probably due toerosion of the sea-bed due to strong bottom-currents(Surlyk & Lykke-Andersen, 2007).
NSCL (Fritsen, 1999) divided UC16dBP into UC16iii,
the base of which is marked by the FDO of Reinhardtities
anthophorus, and UC16ii (pars.; Figure 3). In the schemeof Burnett (1998), the FDO of E. eximius indicates the baseof UC16, virtually coincident with the FDO of R. anthophorus. R. anthophorus was found as a rare occurrence
in one sample within UC16dBP in this study, and was firstfound consistently in UC16aBP. Identification of R. anthophorus can be problematic, as in poorly-preserved ma-Sheldon46

Stage

MaastrichtianThis study

Cribrosphaerella daniae
Zeug. bicrescenticus, Gartnerago segmentatum
Arkh. maastrichtiana
Helicolithus
Nephrolithus frequens
trabeculatus
Lithraphidites quadratus
Seribiscutum primitivum

Tranolithus orionatus,
Reinhardtites levis
Calculites obscurus

Broinsonia parca constricta

Zeugrhabdotus meudinii, Broinsonia parca parca

Heteromarginatus bugensis
Tortolithus caistorensis
Monomarginatus quaternarius,
Reinhardtites anthophorus

Additional observations

N. frequens absent
from intervals within
UC20b-cBP
Increase in P. grandis
abundance

T. hallii, T. pagei
Increase in C. obscurusabundance, L. cayeuxii,
R. levis

Burnett(1998)
non-reworked
Cretaceous taxa

C. daniae
A. maastrichtiana
N. frequens
L. quadratus

R. levis

T. orionatus

B. parca constricta

M. quaternarius
T. caistorensis
H. bugensis
R. anthophorus,
E. eximius

UC20

dBP

cBP
bBP
aBP

UC19

UC18

aBP

bBP

cBP

dBP

UC17

UC16

UC15

“i”

“ii”

“iii”

“i”

“ii”

“iii”

Mortimer(1987)

N. frequens

G. obliquum

N. frequens

N. frequens

G. obliquum,
S. primitivum

B. parca constricta

T. orionatus

R. levis

C. obscurusE. eximius

H. bugensis

B. parca parca

R. anthophorus

B. parca constricta

T. orionatus

R. levis

Z. compactus,
C. obscurusC. daniae

N. frequens,
C. daniae

non-reworked
Cretaceous taxa

Network Stratigraphic in Fritsen(1999)

UC20

UC19

UC18

“i”

“ii”

“iii”

UC17

UC16

UC15

NK1

NK2

NK3

NK4

NK5

NK6

NK7

NK8

Figure 3: Summary of nannofossil data from this study compared with nannofossil events of the boreal biozonations. NB (1) The base Maastrichtian (following Odin, 2001) cannot be
precisely placed; (2) Gartnerago obliquum and Zygodiscus compactus of Network Stratigraphic Consulting Ltd (NSCL; in Fritsen, 1999) are equivalent to Gartnerago segmentatum
and Zeugrabdotus bicrescenticus (this and other studies). The level of the FDO of H. bugensis, according to NSCL, is redrawn to be compatible with that of Burnett (1998)

Camp.

at 294.13m, within UC16dBP, but does not appear again
until 404.76m in UC16aBP. Due to identification difficulties
and its sporadic occurrence, this species is not considered
to be a reliable marker here.
The FDO of Broinsonia parca parca also coincides
with the base of UC16dBP (intra-UC16ii of NSCL; Figure3). In this borehole, the FDO of B. parca parca is at

terial it is difficult to distinguish from R. levis; it is therefore not used as a marker here.
The FDO of Monomarginatus quaternarius defines thebase of UC16dBP (Burnett, 1998). This species is difficult
to distinguish from Misceomarginatus pleniporus under thelight-microscope (J. Lees, M. Hampton, pers. comms,
2007). A single specimen of M. quaternarius was recorded

Upper
Lower
Campanian/Maastrichtianboundary interval
UpperUpper Campanian-Maastrichtian biostratigraphy...Denmark

321.76m and is used in preference over M. quaternarius toapproximate the base of UC16dBP. The FDO of Zeugrhabdotus praesigmoides also coincides with the FDO of B.
parca parca in this study.
The base of UC16cBP is defined by the FDO of Tortolithus caistorensis. The NSCL zonation scheme does not
use T. caistorensis as a marker, as it is very rare and intermittent in North Sea sections. The base of UC16b BP is defined by the FDO of Heteromarginatus bugensis. In thisstudy the FDO of H. bugensis occurs above that of T. caistorensis (Table 1). H. bugensis likely preserves preferentially to Tortolithus spp. (J. Lees, pers. comm., 2008). The
former species is therefore preferred as a marker to Tortolithus spp., meaning that the base of UC16cBP cannot becorrelated in this study (Figure 3). The interval between the
FDO of B. parca parca and the FDO of H. bugensis is referred to UC16b-cBP. The FDOs of T. caistorensis, T. hallii
and T. pageii all occur close to the base of UC16b-cBP. In
this study, T. hallii is the most frequently-noted Tortolithus
species. The FDO of Tortolithus spp. (not exclusively T.
caistorensis) could be used as additional markers within
the Campanian/Maastrichtian boundary interval. R. levis,
L. cayeuxii and C. obscurus increase in abundance downwards in the lower part of this interval.
The observations in this study present some difficulties
in applying only one of the established biozonation
schemes (Figure 3). The relevant part of the UCBP biozonation of Burnett (1998) was erected using sections fromonshore northern Europe, from relatively high and intermediate latitudes, whilst NSCL’s (Fritsen, 1999) and Mortimer’s (1987) schemes were based on offshore material
from the Norwegian and Danish sectors of the North Sea.
Consequently, there may be some palaeobiogeographicaldifferences between the schemes that have not yet been adequately highlighted. In addition, preservation can be quite
variable within the chalk facies, and this can also accountfor apparent discrepancies. With these points in mind, boththe schemes of Burnett (1998) and NSCL (1999) areequally applicable to the Stevns-1 data for the Campanian/Maastrichtian boundary interval and the lower part of
the Lower Maastrichtian. In the Upper Maastrichtian, theBurnett (1998) scheme is more applicabale to the Stevns1 data, although a number of additional events are recognised (Figure 3) that may prove useful in the Danish sectorof the North Sea, or which may have local palaeoenvironmental significance in the Danish region.
5. Conclusions
A thick section (456.10m) of Maastrichtian and Campanian/Maastrichtian boundary interval chalk was penetrated
by the Stevns-1 borehole and belongs to nannofossil subzones UC20dBP-UC16aBP. Thick Maastrichtian sections arerare in NW Europe, and the extensive thickness of the
Stevns-1 core thus allows an expanded biostratigraphic
breakdown. Established nannofossil biozonation schemesof Burnett (1998) and NSCL (in Fritsen, 1999) are both applicable to the present dataset, but additional bioevents are47

found. This dataset represents the results from a single section applicable to the Danish area and could be particularly
useful in linking North Sea sections with onshore sections.
Events of particular note are as follows:
1) The FDO of Gartnerago segmentatum occurs inUC20dBP. The FDOs of Zeugrhabdotus bicrescenticus andHelicolithus trabeculatus occur in UC20cBP.
2) The reliability of Lithraphidites quadratus, Monomarginatus quaternarius, Reinhardtites anthophorus and Tortolithus caistorensis as marker-species is questioned due toidentification problems or scarcity.
3) Prediscosphaera grandis increases in abundance downhole from intra-UC20aBP.
4) The FDO of Calculites obscurus occurs in UC17 in the
Stevns-1 borehole, compared with UC19 in the NSCL
scheme.
5) Together with the FDO of Broinsonia parca parca, theFDO of Zeugrhabdotus praesigmoides may act as a further
marker for the base of UC16dBP.
6) The FDO of Tortolithus spp. (T. caistorensis, T. hallii
and T. pagei) occurs within UC16b-cBP and may prove to be
an additional marker for this interval.
Acknowledgements
Thanks are given to FNU (Danish Natural Science ResearchCouncil), CRC (the Cretaceous Research Centre), GEUS (The
Geological Survey of Denmark and Greenland) and the Department of Geography and Geology, University of Copenhagen for
funding this work. Annette Ryge, Dorthe Samuelsen, Eva
Melskens and Stefan Sølberg (all GEUS) are thanked for technical support. I am grateful to an anonymous reviewer and Jackie
Lees for providing reviews that greatly improved this paper, andto Dave Jutson, Lars Stemmerik, Finn Surlyk and Nicolas
Thibault for commenting on earlier versions.

References
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Crux, J.A. 1982. Upper Cretaceous (Cenomanian to Campanian)calcareous nannofossils. In: A.R. Lord (Ed.). A Stratigraphical Index of Calcareous Nannofossils. British Micropalaeontological Society Series. Chapman & Hall: 81-135.
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Sea Area. Abhandlungen der Geologisches Bundesanstalt, 39:
143–175.
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49

Plate 1
Selected light-micrographs of marker-taxa

5μm
Arkhangelskiella maastrichtiana
Stevns-1, 36.42m

5μm
Calculites obscurus
Stevns-1, 284.81m

5μm
Reinhardtites levis
Stevns-1, 312.57m

5μm
Tranolithus orionatus
Stevns-1, 335.06m

5μm
Z. praesigmoides
Stevns-1, 390.73m

5μm
Broinsonia parca constricta
Stevns-1, 284.81m

5μm
Gartnerago segmentatum
Stevns-1, 113.37m

5μm
Tortolithus caistorensis
Stevns-1, 390.73m

5μm
Zeugrhabdotus bicrescenticus
Stevns-1, 261.77m

5μm

5μm
Broinsonia parca parca
Stevns-1, 335.06m

5μm
Helicolithus trabeculatus
Stevns-1, 174.24m

5μm

5μm
Cribrosphaerella daniae
Stevns-1, 14.29m

5μm
Nephrolithus frequens
Stevns-1, 39.07m

5μm

Tortolithus hallii
Stevns-1, 390.73m

T. hallii
Stevns-1, 390.73m

5μm

5μm

Zeugrhabdotus praesigmoides
Stevns-1, 321.76m

Z. praesigmoides
Stevns-1, 321.76m